Drum drier for sheet material



March 9, 1948. J 5 HILL 2,437,254

DRUM DRIER FOR SHEET MATERIAL Filed Jui so, 1943 INVENTOR. Jokw STANLEYH/LL BY $4M ATTORNEY Patented'Mar. 9, 1948 2,437,254 DRUM DRIER FORSHEET MATERIAL John Stanley Hill, Laurel, Miss, assignor to MasoniteCorporation,

ration of Delaware Laurel, Miss., a corpo- Application July 30, 1943,Serial No. 496,803

4 Claims. (01. 34-410 The invention relates to manufacture of fiberboard products, and particularly to reducing the water content of fibersheets before they are finally dried to thereby get quicker and betterdrying.

Wetlap fiber sheets from the wet machine in which they are formedorldnarily contain about 50-60% of water and are quite thick. The reasonfor this is that, if the pressure on the squeezerolls of the wet machinewere increased much in an effort to reduce water content and thickness,the backward stream of expressed water meeting the lap material enteringthe pinch between the rolls would injure or even cut the lap.

Decrease of water content and increase of compactness of the wetlapgoingto the drier, as a hot air drier of the Coe type, for example, is highlydesirable because the drying time will be shortened in several Ways asfollows: To begin with there is less water to be removed in the drier.The reduced thickness reduces the distance for heat to travel from sheetsurface to sheet center, and the extra compacting reduces theheat-insulating properties of the lap, enabling the heat to traveltherein more readily. Not only is the drying time reduced, but thedrying operation is more controllable and the uniformity of dryness ofthe dried sheets is improved.

and steam from between these foraminous sheets My invention provides aprocess and apparatus for reducing the water content and reducing thethickness of the formed wetlaps in order to obtain beneficial results asabove described when these wetlaps are dried. The drying may be done inan air drier if desired.

However, instead of sending the more highly compacted wetlap to a hotair drier, it may be used for making hardboard and like products bybeing dried in a multiple-platen press with wire mesh in contact withone surface of the sheet. While the removal of extra water from theformed wetlap before sending to the press is not so important in thiscase, it is important to have the wetlap which is introduced into thepress as well compacted and strong as practicable. This is because withmore fragile and softer wetlap, particles and scraps of various kindswould fall from upper sheets on to lower sheets and considerable presstime would be lost by blowing away such particles and pieces of lap withcompressed air, or otherwise removing same, before the boards can bepressed.

In my preferred apparatus and process; the formed wetlaps arepressedbetween heated surfaces with foraminous or porous sheets in contact withthe wetlap and with means, such as wire screen or equivalent, forconducting away water sheets should be of material having low heatconductivity, since with use of material which conducts heat emciently,a skin may be formed on the wetlap which may interfere with later dryingof the sheet.

The general object of the present invention is to provide a process andapparatus for reducing the water content of water-containing fibersheets, known as wetlaps, before subjecting to final drying treatment. v

A further object is to reduce the thickness of the wetlap so as toshorten the distance through which the heat must travel in order toreach the center of the board, and to compact the wetlap so as toincrease the strength and cohesiveness of wetlaps which-are to besubjected to hot-pressing withv wire mesh in contact with the wetlapsurface.

An additional object of the present invention is to reduce the amount ofheat required for drying the wetlap by providing for removal of aconsiderable portion of the water in the liquid phase.

A further additional object of the invention is to provide a process andapparatus whereby the water content of wetlaps may be mechanicallyreduced to a proportion well below the weight of dry fiber, without theexpressed water being so related to the wetlap as to cause injury orcutting thereof.

In the accompanying drawing forming a part of this specification.

Fig. 1 is a diagrammatical, longitudinal, sectional view of a form ofapparatus adapt-ed to carry out my new procedure;

Fig. 2 is an enlarged sectional view on line 2-2 of Fig. 1;

Fig. 3 is a fragmentary sectional view and shows a portion of theforaminous sheet and a screen which is adapted to provide an air spacebetween the foraminous sheet and' the heated pressing means, and

Fig. 4 is a view in section of a modification of my apparatus showingelevations and depressions on the roll surface with cloth and fibroussheet between rolls.

Reference character In designates generally, and more or lessdiagrammatically, a wet machine or sheet-forming machine, l2 a drier,including a tipple l3, and If an intermediately-ar-- ranged apparatusfor partial removal of water from and partial compaction of the wetlapl6.

The head-box l8 of wet machine In receives'watery flbrouspulp from whichthe wetlap i6 is is run on to a travelling Fourdrinler wire 26 to formthe sheet or wetlap I6. This Fourdrinler wire runs around breast roll22, over squeeze rolls 24, 24 and under idler roll 26. A wire screen 23passes around the companion squeeze rolls 3!], 30 and idler 32, thewetlap I6 being interposed and traveled between rolls 24, 24 and 30, 30,and also between screens 20 and 28. The squeeze rolls 24, 24 and 30, 36and suction boxes (not shown) remove a large quantity of water from theformed sheet. A cut-ofl is diagrammatically indicated at 34 for cuttingthe wetlap I6 into suitable board lengths, which are then ready forfurther treatment.

In previous operations, the wetlap I8 was either moved directly intodrier I2, or carried into a heated press on a wire screen (not shown)The feature of providing novel pressure-applying means to removeadditional liquid from the formed wetlap I6 and partly compact the samebefore passing into drier I2 or into a press is the important feature ofthe present invention, and such means is designated generally byreference character I4.

After the fibrous sheets I6 have been cut into proper lengths at 34, thesheets are conveyed between heated pressing rolls 36, 36. The pressingrolls are heated by any suitable heating means, as for example, gasburners 3'I. Belts are interposed between the wetlap I6 and pressingrolls 36, 36. In the drawing endless belts 38 are shown passed aroundrolls 36, 36 and also around idler rolls 40.

The belts 38, 38, as here shown, comprise inner sheets 42 of foraminousmetallic material such as wire screens adapted to afford openings foroutlet of water, steam, vapors, and the like, and also comprise outersheets 44 of foraminous material of low heat conductivity such as cottoncloth, for example, the inner belt sheets 42 contacting rolls 36, andthe outer belt sheets 44 contactlng wetlap I6.

When pressure is applied to wetlap sheets I6 as they are moved betweenthe heated pressing rolls 36, 36, water is forced from the wetlapthrough foraminous sheets 44 and into the airspace formed by the meshformation of screens 42 located between sheets 44, 44 and the rolls 36,36. A considerable portion of the water is immediately transformed intovapor or steam upon contacting heated rolls 36, 36, so that somepressure is built up in the meshes of screen 42. The vapor or steam willthus move towards the region of lower pressure at the ends of the rolls36, 36 as indicated by the directional arrows in Figure 2. As the steametc. moves towards the ends of the rolls, unvaporized water will also beforced out therewith.

The fibrous sheets I6 may be passed between a series of such steam andwater-removing rolls 36, 36 in order to decrease the water contentbefore passing on into drier I2. Three pairs of rolls are here shown.

The following example illustrates the invention by one set of resultsobtained by passing a wetlap containing about 55% of water on weight ofwetlap, or about 122% on weight of dry fiber, between heated rolls, withwire mesh and cotton cloth between the rolls and the wetlap. Steampressure of 150 lbs. per sq. in. was used for heating the rolls, and thepressure between the rolls was about 3800 lbs. per linear inch. Onpassing the wetlap through one pair of rolls at a speed of 32 feet perminute, the moisture content of the sheet 4 was reduced to about 73% ofthe dry weight of the wetlap. The thickness of the sheet was alsomaterially reduced. After three roll passes the moisture was therebyreduced to about 43% of the dry weight of the wetlap. and the thicknessof the sheet was still further reduced.

Another illustration showing the advantage of passing wetlap throughrolls for compaction and moisture reduction is given in the followingexample. A wetlap received from the Fourdrinler machine and containingabout the same percenttage of water as beforewas passed between rolls ata speed of 7 feet per minute, with the same cloth and screen arrangementas before. Steam pressure applied to the rolls was about 140 lbs. persq. in., and linear pressure on the rolls was about 8800 lbs. per inch.After passing through one pair of rolls, the moisture in the fibroussheet was reduced to about 61% on dry weight of fiber. After three rollpasses, the water content had been reduced to about 34% on dry weight offiber.

In the drawing, the air space between the heated rolls 36 and theforaminous sheet of cotton domestic cloth 44 has been shown as formed byscreen wire 42. Similar air spaces or passages to lead vapors andliquids to the atmosphere may be formed by other means, as for example,by providing corrugations or other elevations 46 with intermediatedepressions 48 as shown in Fig. 4 on the surfaces of the rolls which maybe used instead of screen wire.

The method of pressing wet fibrous sheets with a foraminous sheet andhaving air spaces between the heated pressing surface and the foraminoussheet can also be used with flat presses. When flat presses are used,continuous operation as obtained in the case of rolls is not readilypracticable, and for this reason heated rolls are preferred.

The numerous advantages of reducing the water content of fibrous sheetsby the method and apparatus of the present invention will thus beapparent. The foraminous material, which contactsthe fibrous sheet fromwhich the water is being forced, being made of material such as cloth,for example, is of low heat conductivity and will not transfer heat fromthe heated rolls to the wetlap so rapidly as to form a skin on the Isurface of the sheet, which would interfere with removal of water andwith ready penetration of heat to the center of the sheet in subsequentdrying treatment, and if formed in one set of rolls would give rise toblistering in subsequent roll passes. Furthermore, the air space betweensuch foraminous sheet and the heated pressing surface, as the rollsurfaces for example, enables vapors and liquids to be removed via theend regions of the rolls. The water being at least principally removedin this way, water expressed so as to travel backwardly against the lapentering the pinch of the rolls will be minimized and cutting orcrushing of the lap is obviated.

A further advantage which is obtained by the use of the presentinvention consists in better controllability of content of watersolubles in the finished board. If desired, the content of watersolubles can be reduced in about the same proportion as the watercontent of the lap. That is to say, if for example from original ofwater content based on dry weight of fiber, the water in the lap isreduced by my improved method to say 40% on the same basis, the finishedboard would contain only about one-third as much water-soluble materialas in the case where the original wetlap was directly subjected todrying with hot air.

If, however, reduction in water soluble content of the finished boardshould not be desirable, then it would become possible to increase thecontent of water solubles in the suspension of fiber and water which issupplied to the head-box. As for example, if with use of my inventionthe water content of the formed wetlap should be reduced from say 120%to 40% for example on weight of dry fiber, and no reduction in contentof water solubles in the dried board was desired, the concentration ofwater solubles in the pulp in the wet-machine head-box could be threetimes as great as when wetlaps are directly dried without the use of myinvention.

Another advantage which is obtained by the use of the present inventionconsists in the efiective use of resins, particularly thermo-settingresins in fiber boards, Heating of the surface and center portions ofthe lap will be relatively uniform, thus the resins will be uniformlyactivated throughout the thickness of the fibrous sheet. 'This featurewas not possible in previous drying procedures because the resins in thesur-- face portion of the fibrous sheet were activated before heat couldpenetrate into the body portions of the sheet.

Sheets of suitably prepared ligno-cellulose fiber, when treated forpartial removal of water content and partial compaction, and then driedin a hot air drier, as heretofore described, are well adapted for usewith the processes of U. S. patent to Mason No. 2,120,137 and U. S.patent to Mason et al, No. 2,317,394, and for making the product of U.S. patent to Mason 2,234,126,

The examples given are for illustration only and not for limitation ofthe invention, which is 01' the broad scope defined by my claims.

I claim:

1. An apparatus for removing liquids from sheets of fibrous material,which comprises opposed rotatable heated pressing rolls between whichthe sheets are passed, a rotatable idler roll spaced from each pressingroll, an endless belt extending around each pressing roll and around itsassociated idler roll, said endless belts consisting of foraminoussheets of low heat conduc tivity and wire screens, the screens being incontact with the heated rolls and the i'oraminous sheets in contact withthe sheet of fibrous material.

2. An apparatus for removing liquids from sheets of fibrous material,which comprises opposed rotatable heated pressing rolls between whichthe'sheets are passed, a, rotatable idler roll spaced from each pressingroll, an endless foraminous belt having low heat conductivity extendingaround each pressing roll and around its associated idler roll, andmeans to form substantial air spaces between the heated pressing rolland the foraminous belts.

3. An apparatus for removing liquids from sheets of fibrous material,which comprises opposed rotatable heated pressing rolls between whichthe sheets are passed, each pressing roll having elevations anddepressions on the roll surface, a rotatable idler roll spaced from eachpressing roll, and an endless foraminous belt having low heatconductivity extending around each pressing roll and around itsassociated idler roll.

4. An apparatus for removing liquids from sheets of fibrous material,which comprises 0ppwed rotatable heated pressing rolls between which thesheets are passed, each pressing roll having elevations and depressionson the surface of the roll, a rotatable idler r011 spaced from eachpressing roll, and an endless foraminous belt having low heatconductivity extending around each pressing roll and around itsassociated idler roll, said depressions forming air spaces extendingfrom one end of the roll to the opposite end behind the foraminousbelts.

JOHN STI iNLEY HILL.

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